1. Field of the Invention
The present invention pertains to an apparatus and method to extract through pumping, an effluent produced by a drilled well within a geological formation. Preferably, it pertains to the extraction of hydrocarbons. Specifically, the assembly and method comprises the use of continuous coiled tubing capable of transporting effluents to the surface through its interior.
2. Description of the Related Art
Although the demand for liquid hydrocarbons and gas increases, crude oil prices are declining. The reduced prices bring about the need to develop new techniques and methods of artificial lift, and new devices or equipment that reduce the initial investment on a new well, and reduce the lifting cost in new, or even old wells.
Typically, a well is drilled once an underground oil and gas formation or formations are detected. The typical diameter of the drilled hole is about 121/4" in the first 300 feet of borehole, and about 81/2" to total depth or T.D.
Once the borehole is drilled to total depth, the borehole is cased from the surface to the bottom with either 51/2" or 7" steel pipe or casing. The casing is cemented in place by displacing cement through the annular space between the external wall of the casing and the wall of the borehole. Cementing the casing provides firm anchorage of the casing to the borehole and seals the annular space along the entire length of the borehole with the displaced volume of cement.
After the casing has been cemented, the casing is perforated. The perforations are made in the casing at selected elevations or locations according to the nature of the reservoir or reservoirs. The perforations are holes that extend through both the casing wall and the cement sheath in the annular space and allow the free flow of production fluids to the well bore.
In some regions, the pressure of the reservoir, via natural gas, is sufficient to allow the natural lift of the produced fluids to the surface. Such wells are typically identified as "flowing wells." However, reservoirs are, in general, of low pressure, making necessary the use of artificial lift techniques to convey fluids from the well to the surface.
A conventional artificial lift technique comprises a subsurface pump, also called a "rod pump," placed at the bottom of the well. The rod pump is mechanically activated by a string of rods known as "sucker rods" connected on the surface to a walking beam pumping unit. The rod pump and string of sucker rods are deployed or run inside a string of production tubing within the casing. The pumped fluids are conveyed to the surface through the annular space defined by the bore of the production tubing and the string of sucker rods. In conventional wells such as the one described, the production tubing is either 27/8" or 31/2" outside diameter ("OD") and the length of the production tubing string extends from the surface or wellhead to near the bottom of the well.
Among other limitations stated below, sucker rods are subjected to wear due to frictional contact with the wall of the production tubing. The sucker rod wear increases in deviated, slant or crooked holes. Sucker rods in general are subject to mechanical failures either on the rod itself or in the threaded connections joining the individual sections of sucker rods. The various sucker rod failures can result in frequent replacement of the sucker rods. Occasionally, the subsurface pump which needs to be retrieved to the surface for repair. Additionally, the production tubing also requires, from time to time, to be replaced due to mechanical wear or leaking connections.
In the above cases where there has been a failure in the sucker rod string, the subsurface pump, or the production tubing, it is typically necessary to move a rig, commonly referred to as a workover rig or pulling unit, onto the well to pull out of the hole the worn or damaged items for replacement or repair. Typically, workover rigs or pulling units include a derrick provided with working pulleys, a cable drum and drawworks to allow running in or pulling out of the hole the pipe or rods. To keep the cost of service as low as possible, rig up and rig down procedures, as well as going in and out of the hole, needs to be done efficiently and economically. Operations efficiency will also depend on the costs involved to move such rig or rigs from well location to well location, as well as the time involved in making or breaking tubing or sucker rod connections.
Various patents have attempted to reduce the costs involved in well operations. Patent AR 230316 discloses a sucker rod made of fiberglass, whose weight is considerably less, thus requiring less energy for its operation. Patent AR 234862 also discloses the replacement of steel sucker rods by fiberglass rods.
U.S. Pat. No. 5,667,369 to Cholet discloses the replacement of sucker rods with continuous coiled tubing to move the rotor of a progressive cavity pump ("PCP pump") by connecting the bottom end of the continuous coiled tubing to the rotor of the PCP pump. In this case, the rotor of the PCP pump turns by rotating the coiled tubing from the surface. Continuous tubing or coiled tubing weighs less and is easier to handle than sucker rods, although the use of a production tubing string is still necessary in Cholet.
U.S. Pat. No. 4,476,923 to Walling describes a coiled, composite tubing that allows the effluents to be conducted through its interior. The coiled, composite tubing supports an electric activated downhole pump. Electricity is conveyed from the surface to the downhole electric motor through conductors that extend along and through sheaths of the composite tubing. Thus, the composite tubing comprises a complex succession of sheaths wrapped in different materials able to provide the required strength to the composite tubing.
It is desirable to have an assembly and method to pump an effluent produced by a drilled well in a geological formation without the use of typical production tubing and sucker rods. It is further desirable to provide a lighter production string that can be run in the hole and easily retrieved without the need of a derrick, substructure and drawworks.